1. Field of the Invention
The present invention relates to a method for exposing a peripheral area of a wafer and an apparatus for performing the same. More particularly, the present invention relates to a method for precisely exposing a wafer by a predetermined width from a peripheral area to a predetermined inner portion of the wafer coated with photoresist and an apparatus for performing the method.
2. Description of the Related Art
As electronic information media devices, such as computers, become more widely used, semiconductor technology also becomes widely used. From a functional aspect, a semiconductor device is required to operate at a high speed with a large storing capacitance. Accordingly, semiconductor technology has made great strides recently to develop and improve the degree of integration as well as increase reliability and response speed of semiconductor devices. Accordingly, in the field of semiconductor technology, techniques for improving the degree of integration in semiconductor devices, such as photolithographic techniques, which are used as fine processing techniques in manufacturing semiconductor wafers are critical in meeting the current strict requirements and demands in semiconductor manufacture.
As is well known in the field of photolithography technique, a photoresist film is formed on the wafer on which films for forming patterns are deposited. Then, a predetermined portion of the photoresist pattern is removed by exposure and developing processes so that the photoresist pattern is formed on the wafer.
The photoresist film is made of a photosensitive polymer material. The photosensitive polymer material is subject to a chemical reaction by the light, so the solubility of the photoresist polymer material is changed. That is, when the wafer formed with the photoresist film is exposed to the light through a photo mask provided with fine circuits, the chemical reaction selectively occurs in a predetermined portion of the photoresist film, on which the light is radiated, so that the predetermined portion of the photoresist film is changed to non-soluble material or the solubility thereof is Increased as compared with solubility of the other part of the photoresist film. By developing the photoresist film using a film developer, the photoresist pattern is formed. The photoresist pattern may be used as a mask when an etching process or an ion implanting process is carried out.
The photo mask is fabricated such that the photoresist pattern may be formed on a chip area of the wafer. Therefore, a peripheral area of the wafer, in which the chip is not formed, has no photoresist patterns. If the photoresist pattern is formed by using a positive photoresist, which is changed to the soluble material when the light is radiated thereon, the photoresist still remains in the peripheral area of the wafer after the wafer has been developed, since the peripheral area of the wafer is not exposed to the light. The photoresist remaining in the peripheral area of the wafer frequently makes contact with a wafer chuck or a teaser, so the wafer may be contaminated by the photoresist. For this reason, a side rinse process is carried out by spraying a cleaning liquid, such as acetone, on the peripheral area of the wafer to remove the photoresist from the peripheral area of the wafer when the photoresist is coated on the wafer. However, the side rinse process is not capable of completely removing the photoresist remaining in the peripheral area of the wafer.
In an effort to solve at least the above problem, the peripheral area of the wafer is separately exposed and developed after the photoresist pattern is formed on the wafer coated with the photoresist, thereby removing the photoresist from the peripheral area of the wafer.
FIG. 1 illustrates a conventional exposure device for exposing a peripheral area of a wafer.
Referring to FIG. 1, the exposure device for exposing a peripheral area of a wafer has a wafer chuck 12 on which the wafer W formed with a photoresist pattern 10 is loaded. The wafer chuck 12 has a size smaller than a size of the wafer W. A driving section 14 is operatively associated with the wafer chuck 12 to horizontally and rotatably drive the wafer chuck 12. A light source 16 is fixedly installed above the wafer W to radiate the light toward the peripheral area of the wafer W.
In order to expose the entire peripheral area of the wafer W using the conventional exposure device, the wafer is moved by driving section 14 while the light is radiated onto the peripheral area of the wafer W from the light source 16 until the entire peripheral area of the wafer W is exposed to the light.
More particularly, the wafer W formed with the photoresist pattern 10 is loaded on the wafer chuck 12. Then, the light is radiated on a predetermined portion of the peripheral area and an outer area beyond an edge portion of the wafer W. The light is radiated onto the wafer W such that the photoresist film 10 formed on the peripheral area of the wafer W may be exposed to the light.
While the light is being radiated onto the wafer W, the wafer chuck 12 is driven to move the wafer W in such a manner that a predetermined portion of the photoresist film 10 formed on the peripheral area of the wafer W is exposed to the light. The wafer chuck 12 is horizontally driven parallel to a flat zone of the wafer W when the light is radiated onto the flat zone of the wafer W, and is rotatably driven when the light is radiated onto the peripheral area of the wafer W.
However, the above method cannot precisely expose the predetermined portion of the peripheral area of the wafer W. That is, in order to precisely expose the predetermined portion of the peripheral area of the wafer W while rotating the wafer W, a center of the wafer W must precisely match a center of the wafer chuck 12. In addition, the wafer chuck 12 must be horizontally maintained while the rotational operation is being carried out. However, the tolerance may be exceeded when the wafer W is loaded on the wafer chuck 12 by a robot arm or when the wafer chuck 12 is rotated, so precise exposure is difficult
FIG. 2A illustrates a top plan view of a wafer that has been correctly exposed to the light. FIG. 2B illustrates a top plan view of a wafer that has been incorrectly exposed to the light.
The wafer W shown in FIG. 2A has exposed portions 20a and 20b having uniform widths in the peripheral area of the wafer W. However, the wafer W as shown in FIG. 2B has not been uniformly exposed to the light so that widths of exposed portions 20c and 20d of the peripheral area of the wafer W are unevenly formed.
The large width of exposed portion 20d of the wafer shown in FIG. 2B may cause failure of a main chip since a portion of the photoresist pattern formed on the main chip is exposed to the light. In addition, particles may be generated by the photoresist remaining in an area of the exposed portion 20c, thereby also resulting in failure of the chip.
The present invention has been made to solve at least some of the problems of the prior art. Accordingly, it is a feature of an embodiment of the present invention to provide a method for precisely exposing a predetermined portion of a peripheral area of a wafer coated with photoresist.
Another feature of an embodiment of the present invention is to provide an apparatus for performing the method.
To provide the first feature of the present invention, there is provided a method for exposing a peripheral area of a wafer as follows: a photoresist film formed on a peripheral area of a wafer is exposed by radiating a light toward the peripheral area of the wafer while moving the wafer; whether the light is uniformly radiated onto the predetermined width of the peripheral area of the wafer is inspected when the exposing is carried out; and a position of the light to be radiated onto the peripheral area of the wafer is adjusted if the light deviates from the predetermined width of the peripheral area of the wafer.
To provide the second feature of the present invention, there is provided an apparatus for exposing a peripheral area of a wafer. The apparatus includes a wafer chuck on which a wafer formed with a photoresist film is loaded; a first driving section operatively associated with the wafer chuck to drive the wafer chuck; a light source installed above the peripheral area of the wafer to generate light; an inspecting section for inspecting whether the light is precisely radiated from the light source onto the peripheral area of the wafer; and a second driving section operatively associated with both the inspecting section and the light source to drive the light source in such a manner that the light is precisely radiated on the peripheral area of the wafer.
According to the present invention, the photoresist film formed on the peripheral area of the wafer is exposed by radiating the light onto the peripheral area of the wafer while moving the wafer. In addition, the position of the light source is adjusted while inspecting the light radiated onto the peripheral area of the wafer, so that the predetermined width of the peripheral area of the wafer may be precisely exposed.